Portugaliae
Electrochimica Acta

The influence of surface topography and cutting parameters on the corrosion resistance of stainless steel UNS S31600 in a 6% NaCl solution is addressed in the present study. Surface topography has been modified by changing the conditions parameters of superfinish turning, including feed, cutting speed and depth of cut, and their correlations with corrosion resistance have been examined. The results showed that the depth of cut is correlated with the corrosion potential. Moreover, the increase of cutting speed degrades the corrosion resistance and increases the corrosion potential in the anodic phase. In its turn, the polarization resistance increases in a manner correlated with increasing the surface quality.

Use of inhibitor is proven as an efficient and widely accepted corrosion prevention method. Corrosion control of steel is an important activity in technical, economic, environmental and safety terms. This article enumerates several types of inhibitors used to combat corrosion in acidic medium. In this paper, literature on corrosion inhibitors has been reviewed and discussions are made on properties and efficiency of inhibitors. (The prominent features of our work on the mechanism of corrosion inhibitors have been highlighted and in a few cases have tried to predict its mechanism).

The present work has been carried out to study the mechanism of electrochemical degradation of Congo red dye. Electrolysis has been carried out in a single-chamber electrochemical cell having graphite anode and platinum cathode in the presence of KCl as supporting electrolyte under amperostatic conditions. The potential across the electrodes has been adjusted so that a constant 30 mA current passed through the cell. The effect of various operating parameters such as current density, initial dye concentration, nature of supporting electrolyte KCl, pH and electrode materials, on electrochemical degradation of Congo red dye has been investigated. The decolourization efficiency was assessed through UV-Visible studies which are supported by a percentage reduction in Chemical Oxygen Demand (COD). Kinetic studies indicate that decolourization takes place through a second order diffusion controlled reaction. Energy consumption has been calculated. It is observed from Fourier transform infrared spectroscopy (FTIR) and mass spectra that Congo red dye has been degraded to small molecules. Results indicate that electrochemical degradation of Congo red by using low-cost graphite electrodes proves to be an efficient method at an optimum current density of 1.805 mA cm-2.

The inhibition and the effect of temperature and concentration of 1,4-di(1-vinyl-3-methylimidazolium) benzene dibromide (VMIBB) on the corrosion of mild steel in 1.0 M HCl solution was investigated by electrochemical polarization and weight loss experiments at temperatures ranging from 303 to 343 K. The studied inhibitor concentrations ranged between 1.0x10-6 M and 1.0x10-2 M. The percentage inhibition increased with the increase of the inhibitor’s concentration. The percentage inhibition has reached about 93 % at the concentration of 1x10-2 M and 303 K. On the other hand, the percentage inhibition decreased with the increase of temperature. Using the Langmuir adsorption isotherm, the thermodynamic parameters for the adsorption of this inhibitor on the metal surface were calculated. 1,4-di(1-vinyl-3-methylimidazolium) benzene dibromide was found to be a potential corrosion inhibitor, since it contained not only nitrogen, but also three aromatic systems, double bond, and it is a large molecule which has a big surface with high malar surface coverage.

1-(2-Dodecylsulfanyl-ethyl)-1H-imidazole (DSEIm) and 2-Imidazol-1-yl-ethyl-sulfanyl)-acetic acid (ImESAA) were synthesized via radical catalysis method and characterized using 1H NMR and 13C NMR spectroscopy. The corrosion performances of mild steel specimens were studied by three imidazole derivatives include: 1-vinylvinylimidazole (VyIm), DSEIm and ImESAA, which were investigated in 1.0 M HCl using weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) method. The results obtained show that DSEIm is the best corrosion inhibitor; its inhibition efficiency (E %) increases with increasing the inhibitor concentration, but decreases with the raise of temperature. Potentiodynamic polarization studies clearly revealed that the inhibitors changed the mechanism of hydrogen evolution, and that they acted as mixed inhibitors, but most effectively in the cathodic range. The higher values of activation energy (Ea) in the inhibited solution can be correlated with the increased thickness of the double layer; this is interpreted with physical adsorption of the inhibitor onto the metal surface resulting in the formation of a surface film. Adsorption of imidazole derivatives have been studied with Monte Carlo simulations.